HVACopediaCarrier · Air conditioner troubleshooting
Hissing from the outdoor unit after it shuts off
What is going on
On the Infinity 19VS (24VNA9) a hiss is heard at the outdoor unit for a short time after the compressor stops. This is normally the pressure equalizer valve balancing pressures across the rotary compressor so the next start is easier.
Likely causes
- Normal pressure equalizer valve operation during the off cycle
Check in this order
- Confirm the hiss happens right after the compressor stops and fades away on its own.
- Explain to the homeowner that this is a normal sound for this unit, to avoid a callback.
- If the hiss is constant while running, or the system has low capacity or icing, check for a refrigerant leak and check pressures instead - that is not the equalizer valve.
Applies to: Carrier Infinity 19VS variable speed air conditioner 24VNA9
More air conditioner guides
- Amber STATUS or green COMM light not on
- Compressor will not run - winding and electrical checks - Carrier split systems
- Delay before the compressor restarts
- Outdoor unit unresponsive after several faults
- Superheat too high or too low on TXV system - Carrier split systems
- Two-stage unit not changing stages - Carrier 24ANB/25HNB/25HCB6
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Source: Carrier Infinity 19VS Variable Speed Air Conditioner 24VNA9 Application Guideline, catalog 24VNA9---01AG (05/16), Sound section, p.5. Written in our own words; check the manual for your exact model.
For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.